The present invention relates, in general, to a control arm, and to a method of making such a control arm, in particular for use in an undercarriage of a motor vehicle.
German patent publication DE 199 11 121 A1 describes a control arm for use in the undercarriage of a motor vehicle. The control arm includes a connection tube made of an aluminum alloy and having opposite ends formed with mounting eyes. Each mounting eye is composed of a sleeve, which is made of an aluminum alloy and formed with a protruding collar, and a bearing element, which is embedded in the sleeve. The bearing element is made as metallic bushing which includes a rubber element and is press-fitted into a receiving hole of the sleeve.
Press-fitting constitutes a rather complicated and time-consuming process. The metallic bushing has to be precisely secured in place in order to enable a reliable attachment of an undercarriage component. The fabrication of bearing elements is a separate process, whereby a pre-fabricated bearing element includes at least one inner bushing which is encased by a rubber layer. As alternative, several bushings with interposed rubber layers may be provided in such a bearing element. An outer bushing of metal or plastic then surrounds the inner layers. After fabrication, the bearing element is calibrated in the sleeve by a separate step or during the press-fitting process. The inner surface of the receiving hole in the sleeve as well as the outer bushing of the bearing element must have precise tolerances to allow subsequent press-fitting of the bearing element into the sleeve and to realize certain pushing forces. A required pushing force must be defined and maintained to ensure reliability of the press-fit under any occurring forces and environmental conditions over the entire service life.
The conventional control arm suffers many shortcomings. Control arms of aluminum are generally more complex in structure than control arms made of steel. Press-fitting constitutes an additional separate working step. Moreover, the press-fit must have sufficient protection against corrosion under any environmental conditions. Also, the provision of an outer bushing for the bearing element increases the weight of the mounting eye. As a consequence, there is an increase of unsprung masses in an axle system. This may adversely affect the driving comfort of a motor vehicle. The protruding collars of the sleeves of the conventional control arm are made of solid material and engage into the connection tube. Joining between the protruding collars and the connection tube is implemented through a friction stir welding process. This welding process is fairly complicated, when round parts are involved. Moreover, friction stir welding has deficiencies relating to the presence of a hole at the end of the welding process, when the pin-shaped probe is removed. This hole is exposed to increased corrosive stress and significant notch effect, when the control arm is used in an undercarriage. As a consequence, the service life of the control arm is adversely affected.
It is also known to use friction welding for joining a tube to a blunt surface of a block-like or parallelepiped member. However, connection of a thin-walled tube to a large-area block surface poses many problems and results in a significantly increased notch effect. Thus, the life of such a connection is limited so that this type of connection is effectively unsuitable for use in chassis engineering, and moreover the overall weight of the component is also increased.
It would therefore be desirable and advantageous to provide an improved control arm, and method of making such a control arm, to obviate prior art shortcomings and to enable an economical large scale production which results in a smaller weight and yet reliable operation of the control arm.